Embedded micropatterns are used in so-called microelectromechanical systems (MEMS), in which mechanical and electronic components are combined as a component on a substrate. Such MEMS form inertia sensors, gas sensors and micromotors, for example. FIG. 1 shows a diagram of the design of an embedded micropattern with irregular depth profile. The spacing between the basic structure, mostly consisting of silicon, and the surface can be a few hundred μm. The structures also frequently have cavities, or are constructed from different materials.
There are currently no non-destructive methods for characterizing the irregular depth structures of embedded micropatterns which can be used during the production process. The determination of the structure of embedded micropatterns by means of scanning atomic force microscopy (AFM) is, on the one hand, very slow and, on the other hand, severely limited with reference to the determination of the depth of the micropatterns, because deep lying cavities or very irregular depth profiles are inaccessible from the surface. This also holds for the use of the scanning electron microscope (SEM) or the scanning tunneling microscope (STM) whose use additionally destroys the micropattern to be characterized. Procedures based on spectroscopic methods are certainly not destructive, but are limited to the determination of relatively simple patterns on the surface or homogeneous film layers on substrates, because the light normally used for spectroscopy does not penetrate into the regions of the embedded micropatterns of up to 100 μm in depth.
Planar layer systems can be characterized by means of scattered light analysis. The method of ellipsometry, which constitutes a specific form of reflection spectroscopy, is particularly suitable. U.S. Pat. No. 5,910,842 describes a method and a device for determining so-called ellipsometric data of, for example, thin layers on a substrate. Ellipsometry is concerned with the change in the state of polarization of the light during the reflection or scattering of polarized light at a periodically structured surface. FIG. 2 shows a spectrometer S according to the prior art. Here, polarized light is focused from a light source 1 through the polarizer 2 and a focusing unit 3 onto a surface by which it is scattered. The scattered light is reflected onto a detector D via a focusing unit F and the analyzer An. For a given wavelength λ and a fixed angle of incidence φ which is illustrated in FIG. 3, the so-called ellipsometric parameters α(λ) and β(λ) and ψ(λ) and Δ(λ) can be determined from the intensities, determined by the detector D, of the scattered light I(λ, σ) for a given number of polarization planes σ which are determined by the analyzer An;
                                          α            ⁡                          (              λ              )                                =                                                    I                ⁡                                  (                                      λ                    ,                                          0                      ⁢                      °                                                        )                                            -                              I                ⁡                                  (                                      λ                    ,                                          90                      ⁢                      °                                                        )                                                                                    I                ⁡                                  (                                      λ                    ,                                          0                      ⁢                      °                                                        )                                            +                              I                ⁡                                  (                                      λ                    ,                                          90                      ⁢                      °                                                        )                                                                    ,                            (        1        )                                          β          ⁡                      (            λ            )                          =                                            I              ⁡                              (                                  λ                  ,                                      45                    ⁢                    °                                                  )                                      -                          I              ⁡                              (                                  λ                  ,                                      135                    ⁢                    °                                                  )                                                                        I              ⁡                              (                                  λ                  ,                                      45                    ⁢                    °                                                  )                                      +                          I              ⁡                              (                                  λ                  ,                                      135                    ⁢                    °                                                  )                                                                                                                              tan            ⁢                                                  ⁢            ψ                    =                      tan            ⁢                                                  ⁢            σ            ⁢                                                            1                  -                  α                                                                              1                  +                  α                                                                    ,                            (        2        )                                          cos          ⁢                                          ⁢          Δ                =                  β                      1            -                          α              2                                                                      
In the UV/VIS region, the optical constants, specifically the refractive index n and the absorption coefficient k as well as the layer thickness as far as sub-monolayers of atoms and/or molecules of the surface can be determined from the intensities by means of ellipsometric analysis.